Hi! I had the same issue, but managed to solve it. Actually, the sulani elemental ghosts now have TWO options for joining household. One under friendly menu "Invite to join household", that just makes the ghost playable. The other one "Ask to Move In" isn't under any submenu, and this one actually makes the elemental human again and brings up the "split from household and move" pop up. My sim had a small glitch where she wouldn't ask him to move in when I chose this option (the interaction wouldn't show up in the queue), but I cancelled the "chat" interaction and she immediately asked the elemental to move in. Hope this helps you!
